“Supramolecular” materials are materials comprising compounds that are associated via noncovalent bonds, such as hydrogen, ionic and/or hydrophobic bonds. One advantage of these materials is that these physical bonds are reversible, in particular under the influence of temperature or through the action of a selective solvent.
Some of them also have elastomer properties. Unlike conventional elastomers, these materials have the advantage of being able to become fluidized above a certain temperature, thereby facilitating processing thereof, in particular the correct filling of molds, and also recycling thereof.
Moreover, some of these supramolecular polymers consist of molecules bonded in networks exclusively via reversible physical bonds. Despite the relatively modest physical bonding forces of the molecules of such a supramolecular network, these materials are, like classical or conventional elastomers, capable of exhibiting dimensional stability over very long periods of time and of regaining their initial shape after considerable strains. They can be used for manufacturing, for example, leaktight seals, thermal insulating materials, sound-proofing materials, tires, cables, sheaths, soles for footwear, packaging, patches (cosmetic or dermopharmaceutical), dressings, flexible hose clips, vacuum tubes, or else pipes and flexible hoses for conveying fluids.
Supramolecular materials have already been described by the applicant. More particularly, the applicant has already described supramolecular materials having the behavior of elastomers.
A self-healing elastomeric supramolecular material is, moreover, disclosed in document WO 2006/087475. It comprises molecules containing at least three associative functional groups, such as imidazolidone groups, capable of forming several physical bonds and which can be obtained by reacting urea with the product of the reaction of a polyamine with triacids. The materials obtained according to the teachings of documents WO 03/059964 and WO 2006/087475 contain triacids which are covalently linked, via amide functions, to intermediate junctions and/or to end groups, consisting of the product of reacting polyamine with urea and which therefore contain many associative groups, i.e. containing N—H and C═O functions capable of associating with one another via hydrogen bonds. Specifically, the publication by P. Cordier, L. Leibler, F. Tournilhac and C. Soulie-Ziakovic in Nature, 451, 977 (2008) mentions that a polymer synthesized according to the procedure described in document WO 2006/087475 comprises amidoethyl-imidazolidone end groups and di(amidoethyl)urea and diamidotetraethyl triurea junctions. It is understood that, owing to the process for synthesizing these materials, the chemical natures of the abovementioned junctions and end groups are interdependent, in the sense that it is not possible to vary the nature of the amidoethylimidazolidone end group without affecting that of the two junctions.
The document entitled “Versatile One-Pot Synthesis of Supramolecular Plastics, and Self-Healing Rubbers” by Damien Montarnal, François Tournilhac, Manuel Hidalgo, Jean-Luc Couturier, and Ludwik Leibler published in “Journal of the American Chemical Society”, 131 (23): 7966, on Jun. 17, 2009, describes an alternative process for obtaining supramolecular polymers, including those having elastomeric properties of the type of those of the publication by P. Cordier et al. This method makes it possible, inter alia, to break the interdependence of the chemical natures between the junctions and the end groups of the supramolecular network. It thus becomes possible to control the chemical nature of the end groups independently of that of the junctions.
These new self-healing polymers have enormous advantages, such as those of being readily processable, resulting predominantly from renewable raw materials, and of being self-repairing. However, their mechanical properties remain insufficient for many applications of rubbers, in which, in particular, a good balance of the mechanical properties is required. Thus, the self-healing supramolecular polymers described in the prior art exhibit mediocre cold resistance owing to their relatively high glass transition temperature, Tg (close to ambient temperature), low break properties (tensile strength and elongation at break), and slow elastic springbacks after strain.
Some of these faults can be erased by virtue of the formulation, as is widely known to those skilled in the art, in particular by adding fillers such as calcium carbonate, silica or carbon black, or plasticizers, oils and the like. Optionally, these self-healing polymers can also be slightly chemically crosslinked, for example with peroxides. However, the formulation (fillers, plasticizers, oils and the like) and the chemical crosslinking of these new polymers have their limits and are generally reflected by a notable loss of properties, for instance the self-repairing capacity. Thus, for example, although it is possible to increase the tensile strength of a self-healing supramolecular polymer, by adding fillers, this does not have a favorable effect on the cold resistance and the increase in tensile strength remains modest owing to a low filler content necessary in order to preserve optimum self-repair.